I have Vista Home Premium and although the UAC only takes a split second to work, (unlike the 10 seconds you describe) it still does not allow unattended startup of Vista if you have CCleaner set to run on startup. If you don't hit the UAC confirmation, CCleaner eventually gives up.
With the time Vista takes to boot, it's usually handy to make a cup of tea while it does so, and then when you get back with the cuppa, CCleaner has not done its job.
Microsoft hint that the installer should be configured to install with the right level of UAC control, but after several pages of Microsoft-speak I gave up trying to understand it. If UAC is turned off you lose a big security plus in Vista.
By the way Vista is very good since I forced-in SP1 on my Dell Laptop - before that it gave BSOD at least once a day.